This invention relates to a method for the determination of the properties of mouldable materials, such as the granular and pulverous masses of fresh concrete, and stiff liquids, particularly for the determination of the plastic and reologic properties thereof, in which method
a sample of a known weight is taken from the mass, PA1 the sample is subjected to a moulding effect, and PA1 a compression of the sample and the number of working revolutions required therefor are determined.
Bingham's theory on the interdependence between the resistance to deformation and the shear speed of a material can be applied to plastic materials, such as concrete. According to this theory a plastic material has a yield ratio, i.e. a determined minimum shear stress, which is required for obtaining a permanent deformation, and a plastic viscosity dependent on the shear speed.
The measurement of the plastic and reologic properties, such as the yield ratio and the plastic viscosity, would be useful, because the behaviour of concrete both with respect to the castability and the compactibility thereof can be assessed by means of these values. Since the slump of a concrete cone is generally used to describe castability, it has to be taken into account that when using activated plasticizers or silica, the slump value has to be greater than in cases where these additives are not used if the same workability is to be achieved. This is due to the fact that such additives increase the plastic viscosity but not the yield ratio. In other words, concrete containing e.g. silica possesses a normal resistance to deformation at low speeds in slump measurements, but a high resistance at shear speeds occurring during vibration.
For measuring the plastic and reologic properties of plastic concrete masses with different shear speeds, a method is known in which concrete resting freely in a vessel is mixed with several different speeds and the force resisting the mixing is measured. The poorly controlled flows make it necessary to use a nonlinear speed scale. Thereby the shear speed field, too, is strongly non-homogenenous, and no accurate result can be obtained by the measurement if the concretes deviate greatly from each other. Consequently, not even plastic concrete masses can be measured reliably by means of this method.